Medical gasses are used to distend, or insufflate, a body cavity in order to produce a suitable void in the body cavity, which enables a surgeon to perform a minimally invasive surgical procedure on a patient. For example, in laparoscopic surgery or other types of invasive medical procedures one of the surgical goals is to minimize trauma to the tissue surrounding the entry port into the body cavity though the use of a cannula. Typically, during laparoscopic surgery, a surgeon manipulates an instrument inside of the patient through the cannula, which extends through the body tissue and into the body cavity of a patient. Carbon dioxide, which is the most prevalent insufflation gas used in laparoscopic surgery, is also present in the cannula since it flows into the patient's body cavity through the cannula while an insufflator regulates the rate of delivery of the carbon dioxide insufflation gas. Typically, the insufflator, which receives its medical insufflation gas from a medical grade canister, transports the medical insufflation gas to the cannula via a fluid conduit. An oversized cylindrical cannula provides an annular gas flow passage between the interior surface of the cannula, which usually has a cylindrical shape, and the exterior surface of the medical instrument, which also usually has a cylindrical shape.
In order to reduce the trauma to a patient one may want to reduce the diameter of the oversized cannula, which surrounds the medical instrument. Unfortunately, the reduction of the diameter of the oversized cannula, which is beneficial since it reduces trauma around the tissue pierced by the cannula, causes other problems since the medical devices and surgical instruments introduced into a lumen in the cannula increase the obstruction to the flow of the insufflation gas that enters the body cavity through the same lumen in the cannula. If a small surgical instrument is placed within a cannula of reduced diameter the flow obstruction may not be significant, however, with the use of larger and more complex surgical instruments in a cannula, which is no longer oversized, the pressure losses or pressure drop created by the annular like passage located between the interior surface of the cannula and the exterior surface of the medical instrument may have adverse consequences if one wants to maintain the body cavity in an inflated condition as well as the medical instrument in a sealed relationship to the cannula.